Fossiliferous Limestone (Crinoidal Limestone)

Physical Properties

Hardness: 3 (Mohs scale); Color: Brown to tan matrix with white fossil inclusions; Luster: Dull/Earthy; Crystal structure: Macro-fossiliferous; Reaction: Effervesces with dilute hydrochloric acid.

Formation & Geological History

Formed in shallow, calm marine environments whereby the remains of marine organisms, specifically crinoids (sea lilies) and brachiopods, settled on the seafloor and were lithified over millions of years. This specimen likely dates from the Paleozoic era.

Uses & Applications

Used primarily for fossil collecting, educational purposes, and as a decorative stone. Large deposits are used in the production of cement and crushed stone for construction.

Geological Facts

The white circular and 'donut' shapes visible are cross-sections of crinoid stems, which were animals related to starfish, not plants. They were so abundant in ancient seas that they often formed entire rock layers.

Field Identification & Locations

Identify in the field by looking for distinct white circular or screw-like patterns (fossil stems) embedded in a finer-grained matrix. It is commonly found in areas of the Midwest US, UK, and other regions with exposed ancient seabed strata.

Identified on: 4/24/2026

Mode: Standard